Pick up tube with infra-red sensitive thermionic cathode with cooling means spaced from the thermionic cathode



July 25, 1967 (3. A4 MORTON ETAL Filed April 15, 1948 #5014 ,zoml 7 2000M50 3,333,133 PICK UP TUBE WITH INFRA-RED SENSITIVE THERMIONIC CATHODEWITH COOLING MEANS SPACED FROM THE THERMIONIC CATHODE I l I I l I I I II I I I I I I I I I I I I I Smaentor:

EIEIIIREE A-MDRTDN WMM 3 EAHDNERL .KRIEEER (I IIorneg United StatesPatent PICK UP TUBE WITH lNFRA-RED SENSITIVE THERMIONIC CATHODE WITHCOOLING MEANS SPACED FROM THE THERIVIIONIC CATHODE George A. Morton andGardner L. Krieger, Princeton, N."J., assignors, by mesne assignments,to the United States of America as represented by the Secretary of theArmy Filed Apr. 15, 1948, Ser. No. 21,156 Claims. (Cl. 313-65) Thisinvention relates to devices for observing objects in the dark by meansof infra-red radiant energy particularly in the wave spectrum 8 to 13microns called far infra-red.

In prior art image devices it has been the practice to use aphoto-cathode that is from time to time sensitized by ultra violet lightto store energy. This is stimulated by near infra-red energy to emitvisible light. The infrared energy does not in this type of cathodeproduce the light by direct action on the atomic structure of thephosphor but indirectly through release of energy previously stored inthe cathode by the energy of shorter wave lengths.

It is an object of this invention to provide an image de vice thatproduces an electron image by producing thermal changes in the cathode.

Another object of the invention is to produce an image device having athermionic cathode acted upon by far infra-red energy to releaseelectrons which are in turn imaged to form a greatly demagnifiedelectron image on a fluorescent screen in order to increase theintrinsic brightness.

Another object of the invention is to bias the thermionic cathode of animage device to relatively low temperature to increase the effect of farinfra-red energy in relation to that of the ambient temperature.

Other objects of the invention will appear in the followingspecification, reference being had to the drawing in which:

The single figure is a sectional elevation of an image device embodyingthe invention.

This invention relates to a heat which the photocathode is provided heatinertia transparent foundation, such as a thin sheet of glass so thatthermionic emission from the cathode develops the electron image whichis utilized in a conventional manner upon a fluorescent screen.

sensitive image tube in on a very thin low- The thermionic properties ofphotocathodes of the type 4 described below are well known. The tube ofthe invention is dependent upon the heating of elemental areas of thecathode with an infra-red image while maintaining the photocathode ofthe tube cooled to provide normal thermionic emission at a low thermallevel relative to ambient temperature. By this means, then, the effectof far infra-red energy in relation to that of ambient temperature isdetectable.

Referring to the drawing, the image device comprises an evacuated tubeenvelope 1 of glass or other suitable material which has a window 2 ofsome material such as rock salt transparent to far infra-red energy. Ametal cathode cylinder 3 has a very thin film or sheet of glass 4, ofother suitable material, secured across one end of the cylinder adjacentthe window 2. The glass film 4 has a layer or coating 5 of thermionicemitting material such as caesiated silver-silver oxide, well known inthe art. Other materials may, however, be used. The glass film andcoating absorb infra-red energy to produce a rise in temperature atpoints illuminated by the infra-red radiations and cause the thermioniccoating 5 to emit electrons by thermal action. The number of electronsemitted vary with the impinging infra-red energy so that an electronimage will be produced corresponding to any infrared image focused onthe film 5. Various voltages and dimensions may be used for the cathodecylinder 3, but, as an example, suitable values will be given for thisand the other electrodes in the tube shown.

The cathode cylinder 3 may have a diameter of 1.3 inches and a length of0.25 inch. It is connected to the negative terminal of the voltagesupply. Spaced about 0.0625 inch from the end of cylinder 3, is anodecylinder 6 having a diameter of about 1.2 inches and a length 0.375inch. This anode may be connected to a terminal of the voltage supplywhich is 150 volts positive with respect to the cathode cylinder 3.Tubular anode 7 is spaced about 0.0625 inch from anode 6 and may have adiameter of about 1.1 inches at the end adjacent anode 6 and a flangedother end 8 having an opening of 0.375 inch. This anode may be 0.875inch in length and is connected to a terminal of the supply which is 200volts positive with respect to the cathode 3. Anode 9 is spaced about0.125 inch from flanged end 8. The diameter of this anode at the endfacing the anode, is about 0.375 inch. Also, this end of anode 9 mayhave an external flange 10 and the other end an internal flange ordiaphragm 11 having an aperture of about 0.15 inch. This anode may beconnected to a terminal 2000 volts positive relative to the cathode 3. Adiaphragm 12 having an aperture of about 0.15 inch is spaced about .0625inch from the diaphragm 11 and may be connected to the 880 voltterminal. Anode 13 has a diaphragm 14 at the end spaced about 0.0625inch from diaphragm 12 and also has an aperture of about 0.15 inch. Theother end of anode 13 is open and may be spaced about 0.0625 inch from aphosphor screen 15 on the transparent end plate 16 of the tube envelope.Anode 13 may 'be connected to a terminal of the voltage supply which is6000 volts positive relative to cathode 3. The screen 15 may be of anyappropriate phosphor material such as zinc sulphide or zinc silicate.

To cool the cathode to a low temperature of about -20 C. to C., orlower, the cathode end of the tube envelope is surrounded by a jacket 17connected by an inlet 18 to a tank (not shown) containing liquid air orcarbon dioxide gas under high pressure. The jacket 17 is vented at 19 tothe atmosphere. Upon adjustment of the expansion of the CO gas by needlevalve 20, the temperature of the thermionic cathode 5 may be regulated.The cooling jacket 17 may be closed by a pair of glass or plastic plates30 and 32 which are transparent to infra-red. Plates 30 and 32 arespaced apart and prevent fogging of the tube window 2 when cooling gasis passed into the jacket 17. Plates 30 and 32 may be of any appropriatematerial which will transmit the desired infra-red radiation. The tubeenvelope 1 may also be surrounded, except for end 16, by another coolingjacket 34 connected to the intake 18 and having an outlet 36 formaintaining the envelope 1 at a relatively low temperature. Jackets 17and 34 may be combined to form a single cooling chamber.

The image tu'be may be used with the well known Schmidt optical systemhaving a spherical mirror 22, a corrector plate 23, made of infra-redtransmitting material, and a mirror 24. The far infra-red energy isfocused as at 25 on the thermionic cathode 5 and electrons are emittedfrom each elemental area of surface 5 in proportion to radiant energyfocused on the area element. The electrons are then focused on thephosphor screen 15 by the electrostatic lens system of anodes 6, 7, 9,12 and 13 to produce a demagnified image of about one tenth the size ofthe image formed on cathode 5. The image may be reduced to any desiredsize by suitably altering the dimensions of the electrodes and voltagesapplied thereto. The reduction of the image in this way proportionallyincreases the intrinsic brightness and the image on screen may be inturn optically magnified. The supports for the various electrodes arenot shown as these are well known in the art and are shown in myapplication filed jointly with Flory and Reudy, Oct. 5, 1946, Ser. No.701,588 which is now Patent No. 2,506,- 018, granted May 2, 1950.

Various modifications may be made of the invention without departingfrom the spirit thereof.

What we claim as new is:

1. An electron image tube comprising an evacuated envelope including atone end thereof a window transparent to infra-red radiant energy, atubular cathode within said envelope having one end adjacent saidwindow, a film substantially transparent to said infra-red energymounted across said one end of said tubular cathode, a phosphor screenmounted at the other end of said envelope, a thermionic cathode on theside of said transparent film facing said phosphor, a plurality of anodeelectrodes positioned between said thermionic cathode and said phosphorscreen for focusing electrons from said thermionic cathode, and meansspaced from said transparent film to cool said thermionic cathode onsaid phosphor screen below ambient temperature.

2. An electron image tube comprising an evacuated envelope including awindow transparent to infra-red radiant energy, a cathode cylinderwithin said envelope having one end adjacent said window, a sheet ofmaterial substantially transparent to said infra-red energy mountedacross said cathode cylinder, a phosphor screen at the other end of theenvelope intercepting the axis of said cathode cylinder, a thermioniccathode on the side of said sheet facing said phosphor screen, aplurality of anode electrodes positioned between the thermionic cathodeand said phosphor screen, for electrostatically focusing an electronemission from'said thermionic cathode on said phosphor screen, and meansspaced from said thermionic cathode to cool portions of said tubeadajacent said thermionic cathode below the temperature of the ambientatmosphere.

3. An electron image tube comprising an evacuated envelope having aportion thereof transparent to infra-red radiations, a thermioniccathode electrode mounted within said envelope spaced from and adjacentsaid transparent envelope portion, a phosphor screen within saidenvelope spaced from said cathode electrode, means between said cathodeelectrode and said phosphor screen for accelerating and focusing anelectron emission from 4 cathode electrode onto a reduced portion ofsaid screen, and a cooling chamber including said transparent envelopeportion for maintaining the thermionic cathode below the temperature ofthe ambient atmosphere.

4. An electron image tube comprising an evacuated tubular envelopehaving each end thereof closed by a transparent wall portion, athermionic cathode electrode mounted at one end of said tubular envelopespaced from and adjacent to said wall portion closing said one end ofsaid envelope, a phosphor material coating said Wall portion closing theother end of said tubular envelope, means between said thermioniccathode and said phosphor coating for focusing an electron emission fromsaid cathode on said phosphor film, a cooling chamber including saidwall portion at said one end of said envelope for maintaining said oneend of said envelope below the 7 temperature of the ambientatmosphere,,said chamber including a window comprising a pair of thinplates transparent to infra-red radiations.

5. An electron image tube comprising an evacuated tubular envelopehaving each end thereof closed by a transparent wall portion, athermionic cathode electrode mounted within one end of said tubularenvelope spaced from and adjacent to said wall portion closing said oneend of said envelope, a phosphor material coating said wall portionclosing the other end of said tubular envelope, means between saidthermioniccathode and said phosphor coating for focusing an electronemission from said cathode on said phosphor film, a cooling. chamberenclosing said tubular envelope for maintaining .said image tube belowthe temperature of the ambient atmosphere, said chamber including awindow extending over said one end of saidenvelope, said windowcomprising a pair of thin plates transparent to infra-red radiations.

References Cited UNITED STATES PATENTS 1,955,899 4/1934 vZworykin250-164 X 2,107,782 2/1938 Farnsworth et al 315-11 2,189,319 2/1940Morton 250-153 X 2,206,387 7/1940 Bruche 250-153 2,227,030 12/ 1940Schlesinger 250-166.l 2,234,328 3/1941 Wollf 250-153 FOREIGN PATENTS139,313 8/ 1930' Switzerland.

JAMES W. LAWRENCE, Primary Examiner. JAMES L. BREWRI'NK, Examiner.VINCENT LAFRANCHI, Assistant Examiner.

1. AN ELECTRON IMAGE TUBE COMPRISING AN EVACUATED EVELOPE INCLUDING ATONE END THEREOF A WINDOW TRANSPARENT TO INFRA-RED RADIANT ENERGY, ATUBULAR CATHODE WITHIN SAID ENVELOPE HAVING ONE END ADJACENT SAIDWINDOWN, A FILM SUBSTANTIALLY TRANSPARENT TO SAID INFRA-RED ENERGYMOUNTED ACROSS SAID ONE END OF SAID TUBULAR CATHODE, A PHOSPHOR SCREENMOUNTED AT THE OTHER END OF SAID ENVELOPE, A THERMIONIC CATHODE ON THESIDE OF SAID TRANSPARENT FILM FACING SAID PHOSPHOR, A PLURALITY OF ANODEELECTRODES POSITIONED BETWEEN SAID THERMIONIC CATHODE AND SAID PHOSPHORSCREEN FOR FOCUSING ELECTRONS FROM SAID THERMIONIC CATHODE, AND MEANSSPACED FROM SAID TRANSPARENT FILM TO COOL SAID THERMIONIC CATHODE ONSAID PHOSPHOR SCREEN BELOW AMBIENT TEMPERATURE.